Diseases of the cardiovascular system affect millions of people each year and are a leading cause of death throughout the world. The cost to society from such diseases is enormous both in terms of the number of lives lost as well as in terms of the costs associated with treating patients through traditional surgical techniques. A particularly prevalent form of cardiovascular disease is caused by atherosclerosis, a form of arteriosclerosis.
Atherosclerosis is a disease in which the lumen (interior passage) of an artery becomes stenosed (narrowed) or even totally occluded (blocked) by an accumulation of fibrous, fatty, or calcified tissue. Over time this tissue, known in medicine as an atheroma, hardens and occludes the artery. The partial stenosis or full occlusion of the coronary arteries that supply the heart muscle leads to ischemia (deficient blood flow) of the heart muscle, angina (chest pain), and can lead to infarction (heart attack) or patient death. Although drug therapies and modifications to diet and lifestyle show great promise for preventing and treating atherosclerotic vascular disease, many patients urgently require restoration of blood flow that has already been lost, especially in those having severely or totally occluded blood vessels.
In many cases, a patient suffering a coronary vessel obstruction or restriction undergoes a coronary artery bypass graft (CABG) surgical procedure, more commonly known as a “heart bypass” operation to restore normal oxygenated blood flow to the heart muscle downstream of the obstruction or restriction. More particularly, a fluid connection or “distal anastomosis.” is surgically established between a source vessel of oxygenated blood and the obstructed or restricted target coronary artery downstream or distal to the obstruction or restriction to restore the flow of oxygenated blood to the heart muscle. In one approach, the surgeon attaches an available source vessel, e.g., an internal mammary artery (IMA), directly to the obstructed target coronary artery at the distal anastomosis site downstream from the obstruction or restriction.
There are a number of alternative approaches to CABG surgery. In one approach, the surgeon harvests a graft blood vessel from the patient's venous system and prepares its proximal and distal ends to be attached in a “proximal anastomosis” and a “distal anastomosis” bypassing the occlusion. This type of graft is commonly known as a “free” graft. The proximal anastomosis can be located proximal or upstream to the occlusion or to another vessel supplying oxygenated blood, e.g., the aorta. Typically, a section of the saphenous vein is harvested from the patient's body. Sometimes, the internal mammary artery (IMA) is used as the graft blood vessel or the radial artery is used as arterial conduit and the proximal anastomosis has to be made. In another approach, artery-to-artery bypass procedures have been utilized in which an arterial source of oxygenated blood, e.g., the left IMA or right IMA, is severed and a portion is dissected away from supporting tissue so that the severed end can be anastomosed to the obstructed coronary artery distally to the stenosis or occlusion. More recently, other arteries have been used in such procedures, including the inferior epigastric arteries and gastroepiploic arteries. It is also stated in U.S. Pat. No. 6,080,175 that a conventional electrosurgical instrument can be introduced through a port or incision and used to dissect and prepare the bypass graft vessel for coronary anastomosis while viewing the procedure through a thoracoscope.
It is necessary to access and prepare the site or sites of the vessel wall of the target coronary artery where the proximal and/or distal anastomosis is to be completed and to then make the surgical attachments of the blood vessels. First, it is necessary to isolate the anastomosis site of the target coronary artery from the epicardial tissues and overlying fatty layers. Typically, blunt, rounded #15 scalpel blades are employed to dissect these tissues and layers away from the target coronary artery.
Generally, blood flow in the target coronary artery is interrupted by, for example, temporary ligation or clamping of the artery proximal and distal of the anastomosis site, and the target coronary artery wall is opened to form an arteriotomy, that is, an elongated incision at the anastomosis site extending parallel to the axis of the coronary vessel and equally spaced from the sides of the coronary artery that are still embedded in or against the epicardium. The arteriotomy is typically created by use of a very sharp, pointed, #11 scalpel blade to perforate the coronary artery wall, and the puncture is elongated the requisite length using scissors. A “perfect arteriotomy” is an incision that has straight edges, that does not stray from the axial alignment and equal distance from the sides of the coronary artery, and is of the requisite length.
Similarly, it is necessary to prepare the attachment end of the source vessel by cutting the source vessel end at an appropriate angle for an end-to-side or end-to-end anastomosis or by forming an elongated arteriotomy in the source vessel wall of a suitable length that is axially aligned with the source vessel axis for a side-to-side anastomosis. Typically, the surgeon uses surgical scalpels and scissors to shape the source vessel end or make the elongated arteriotomy slit in the source vessel, and uses sutures or clips to close the open severed end.
In the example depicted schematically in FIG. 1, the heart 12 is prepared as described above for an end-to-side anastomosis of the surgically freed, severed, and appropriately shaped vessel end 31 of the left IMA 30 branching from the aorta 16 and left subclavian artery 18 to the prepared arteriotomy 15 in the vessel wall of the left anterior descending (LAD) coronary artery 14 downstream from the obstruction 38. Similarly, in the example depicted schematically in FIG. 3, the heart 12 is prepared as described above for a side-to-side anastomosis of the left IMA 30 to the prepared arteriotomy 15 in the vessel wall of the LAD coronary artery 14. In the side-to-side anastomosis, an arteriotomy 33 is made in the freed segment of the left IMA 30, and the vessel end 31 is sutured closed.
The prepared end or elongated arteriotomy of the bypass graft or source vessel is attached or anastomosed to the target coronary artery at the arteriotomy in a manner that prevents leakage of blood employing sutures, staples, surgical adhesives and/or various artificial anastomosis devices. For example, an end-to-side anastomosis 35 of the shaped vessel end 31 of the left IMA 30 to the prepared arteriotomy 15 in the vessel wall of the LAD coronary artery 14 is illustrated in FIG. 2. And a side-to-side anastomosis 37 joining the arteriotomy 33 of the left IMA 30 to the prepared arteriotomy 15 of the LAD coronary artery 14 is illustrated, for example, in FIG. 4.
The inner, endothelial layer, vessel linings are less thrombogenic than the outer epithelial layers of blood vessels. So, in one approach, the attachment is made by everting and applying the interior linings of the bypass graft or source vessel and the target coronary artery against one another and suturing or gluing or otherwise attaching the interior linings together. Various types of artificial biocompatible reinforcement sleeves or rings, e.g., those shown in the above-referenced '369 patent can also be used in the anastomosis. Currently, a number of mechanical anastomotic devices, materials, techniques, and procedures are being developed for facilitating the process of forming an anastomosis including vascular clips or staplers, glues, adhesives or sealants, laser welding, mechanical couplers, stents and robot-assisted suturing. These techniques are being developed for performing end-to-end, end-to-side and/or side-to-side anastomoses with or without temporary blood flow interruption. In general, these techniques can include the use of various biomaterials and/or biocompatible agents. See, for example, U.S. Pat. Nos. 5,385,606, 5,695,504, 5,707,380, 5,972,017 and 5,976,178, and 6,231,565.
Various examples of forming the target vessel arteriotomy or arteriotomies, the shaped end or side wall arteriotomy of the source vessel, and the positioning and attachment of the source vessel and target artery together are set forth in U.S. Pat. Nos. 5,776,154, 5,799,661, 5,868,770, 5,893,369, 6,026,814, 6,071,295, 6,080,175, 6,248,117, 6,331,158, and 6,332,468.
In a conventional bypass graft or CABG procedure, the surgeon exposes the obstructed coronary vessel through an open chest surgical exposure or thoracotomy providing direct visualization and access to the epicardium. Typically, fat layers that make it difficult to see either the artery or the occlusion cover the epicardial surface and the obstructed cardiac artery. However, surgeons are able to dissect the fat away to expose the artery and manually palpate the heart to feel the relatively stiff or rigid occlusion within the artery as a result of their training and experience. The surgeon can determine the location and length of the occlusion as well as suitable sites of the target coronary artery for the proximal and distal anastomoses with some degree of success.
The open chest procedure involves making a 20 to 25 cm incision in the chest of the patient, severing the sternum and cutting and peeling back various layers of tissue in order to give access to the heart and arterial sources. As a result, these operations typically require large numbers of sutures or staples to close the incision and 5 to 10 wire hooks to keep the severed sternum together. Such surgery often carries additional complications such as instability of the sternum, post-operative bleeding, and mediastinal infection. The thoracic muscle and ribs are also severely traumatized, and the healing process results in an unattractive scar. Postoperatively, most patients endure significant pain and must forego work or strenuous activity for a long recovery period.
Many minimally invasive surgical techniques and devices have been introduced In order to reduce the risk of morbidity, expense, trauma, patient mortality, infection, and other complications associated with open chest cardiac surgery. Less traumatic limited open chest techniques using an abdominal (sub-xyphoid) approach or, alternatively, a “Chamberlain” incision (an approximately 8 cm incision at the sternocostal junction), have been developed to lessen the operating area and the associated complications. In recent years, a growing number of surgeons have begun performing CABG procedures performed while the heart is still beating using minimally invasive direct coronary artery bypass grafting (MIDCAB) surgical techniques and devices. Using the MIDCAB method, the heart typically is accessed through a mini-thoracotomy (i.e., a 6 to 8 cm incision in the patient's chest) that avoids the sternal splitting incision of conventional cardiac surgery. A MIDCAB technique for performing a CABG procedure is described in U.S. Pat. No. 5,875,782, for example.
Other minimally invasive, percutaneous, coronary surgical procedures have been advanced that employ multiple small trans-thoracic incisions to and through the pericardium, instruments advanced through sleeves or ports inserted in the incisions, and a thoracoscope to view the accessed cardiac site while the procedure is performed as shown, for example, in the above-referenced '175, '295, '468 and '661 patents and in U.S. Pat. Nos. 5,464,447, and 5,716,392. Surgical trocars having a diameter of about 3 mm to 15 mm are fitted into lumens of tubular trocar sleeves or ports, and the assemblies are inserted into skin incisions. The trocar tip is advanced to puncture the abdomen or chest to reach the pericardium, and the trocar is then withdrawn leaving the port in place. Surgical instruments and other devices such as fiber optic thoracoscopes can be inserted into the body cavity through the port lumens. As stated in the '468 patent, instruments advanced through trocars can include electrosurgical tools, graspers, forceps, scalpels, electrocautery devices, clip appliers, scissors, etc.
In the above-described procedures, the surgeon can stop the heart by utilizing a series of internal catheters to stop blood flow through the aorta and to administer cardioplegia solution. The endoscopic approach utilizes groin cannulation to establish cardiopulmonary bypass (CPB) and an intraaortic balloon catheter that functions as an internal aortic clamp by means of an expandable balloon at its distal end used to occlude blood flow in the ascending aorta. A full description of an example of one preferred endoscopic technique is found in U.S. Pat. No. 5,452,733, for example.
However, recently developed, beating heart procedures eliminate the need for any form of CPB, the extensive surgical procedures necessary to connect the patient to a CPB machine, and to stop the heart. A number of surgical instruments have been developed that attempt to stabilize or immobilize a portion of the beating heart that supports the target coronary artery and the anastomosis site. These beating heart procedures described, for example, in the above-referenced '158, '175, '770, '782, and '295 patents and in U.S. Pat. Nos. 5,976,069, and 6,120,436, can be performed on a heart exposed in a full or limited thoracotomy or accessed percutaneously.
For example, a retractor assembly disclosed in the above-referenced '158 patent mounts to and maintains the chest opening while supporting a stabilizer assembly that extends parallel stabilizer bars against the epicardium alongside the target coronary artery so that force is applied across the anastomosis site to suppress heart motion. The surgeon employs conventional manually applied clamps to block blood flow through the arterial lumen and scalpels and scissors to make the elongated incision of the arteriotomy.
Instruments are disclosed in the above-referenced '295 patent that apply suction to the epicardial surface around or alongside the anastomosis site to suppress heart motion. Again, the surgeon employs the conventional manually applied clamps to block blood flow through the arterial lumen and a scalpel to make the elongated incision of the arteriotomy.
Instruments that combine the application of suction to the epicardial surface around or alongside the anastomosis site to suppress heart motion with a cutting mechanism for making the arteriotomy are disclosed in the above-referenced '175 and '770 patents. The surgical cutting instruments disclosed in the '770 and '175 patents include an elongated shaft having a proximal end, a distal end adapted for percutaneous insertion against the target coronary artery over the anastomosis site, and an axial lumen therebetween. A suction pad is formed at the distal end of the shaft, and a cutting element disposed within the lumen of the shaft near the distal end. A vacuum line is fluidly coupled to the lumen of the shaft and is adapted to connect to a vacuum source to effect a suction force at the distal end of the shaft. A control mechanism is provided to selectively block flow between the vacuum source and the lumen. The control mechanism may include a slide valve, an on/off button, or other equivalent mechanism for selectively closing and opening the vacuum pathway. A gripper assembly configured to grip a portion of the coronary artery is also disclosed in the '175 patent.
The cutting element and the shaft are relatively moveable between a retracted position and a cutting position. The cutting element is adapted to make the elongated slit of the arteriotomy in alignment with the axis of the coronary artery when the cutting element and the shaft are in the cutting position and the vacuum holds the anastomosis site steady.
The distal end of the shaft disclosed in the '175 patent has an outside diameter of less than about 5 mm, and the cutting element comprises at least one cutting element having a substantially straight blade cutting edge. The cutting edge is displaced at an angle of between about 15 to 30 degrees relative to a vertical axis through the cutting element. In one embodiment, the cutting element is fixed to an actuator push rod located within the lumen of the shaft, and connected to an actuator, preferably an actuator button, at a proximal end thereof. In another embodiment, the shaft is slidably mounted to a handle of the cutting instrument. An anchor, preferably a rigid rod coaxially disposed within the shaft, fixes the cutting element to the handle. An actuator member mounted to the shaft and biased by a spring is actuated to slide the shaft between retracted and cutting positions with respect to the cutting element.
Additionally or alternatively, at least one electrode may be disposed near the distal end of the shaft to effect or enhance cutting. The electrode may be operatively coupled to the cutting element, preferably substantially co-linearly coupled to the cutting edge. In the depicted embodiments, the electrode extends to the sharpened tip of the cutting element opposite to the cutting blade. In use, the end of the electrode at the tip of the cutting element is placed against the coronary artery and energized by radio frequency energy as the cutting element is moved to the cutting position to facilitate making a small point incision or pilot hole in the coronary artery. Then, the cutting blade is fully advanced to make the elongated cut. Ultrasonic energy may be applied to the cutting element to effect or enhance cutting by the ultrasonically vibrating the cutting blade.
All of the above-described approaches employ a cutting blade to make the elongated slit of the arteriotomy. In most cases, the shaft must be carefully moved to advance the cutting blade along the length of the vessel wall without inadvertently pushing the tip of blade across the vessel lumen and through the vessel wall opposite to the intended slit. Damage can be caused to the vessel wall if care is not taken.
A vessel wall cutting instrument or tool is needed for making an arteriotomy or a similar slit in a vessel wall is needed that avoids or minimizes the need to move the cutting tool or the cutting blade along the vessel wall to slit the vessel wall to a desired length.
A vessel wall cutting instrument or tool is needed that does not inadvertently advance across the vessel wall from the slit and damage the vessel wall opposite to the slit.
A vessel wall cutting instrument or tool is needed that enables occlusion of the blood vessel to inhibit blood loss through the incision as the incision is being made.
A vessel wall cutting instrument is also needed that can make a clean straight incision of predetermined length and width in a vessel wall quickly within the time between heart contractions.